A number of structures with very high strength-to-weight ratios have been developed for special applications, such as aircraft and aerospace uses. Some of these structures, typically fabricated from metals such aluminum and titanium, rely on very weight efficient configurations to obtain the desired strength, stiffness, etc. One well-known configuration, called isogrid, has upstanding ribs generally integral with the skin (or membrane) material and arranged in a repeating pattern of equilateral triangles that touch the other equilateral triangles along shared sides and at corners of the triangles in an isogrid configuration. The intersections of the stiffeners where the corners of the triangles touch are typically called nodes, and are often used as attachment points for secondary structures. Isogrid and similar stiffener configurations, such as orthogrid, are the most common designs employed for integrally grid-stiffened panels. Such grid-stiffened structural supports can be used to fabricate a variety of vehicle parts, for example, fuel tanks and load-bearing aerospace panels. Standard isogrid, orthogrid, and other grid-stiffened panel applications are typically designed to prevent local buckling and global buckling.
Local buckling can manifest itself as crippling of the stiffeners and pocket buckling of the skin, and global buckling is typically characterized as a general, large scale collapse of the structure. Weight optimization of grid-stiffened structures to prevent local buckling tends to bias panel design towards small pocket sizes (stiffeners spaced close together) and smaller stiffeners, while global buckling biases the panel towards larger pocket sizes and larger, more efficient stiffeners. As such, local and global buckling are at odds with respect to the panel dimensions, and typical grid-stiffened panels are a compromise between preventing local and global failure.
To increase the performance of aerospace structures, there is a need for improved isogrid and orthogrid structures that prevent buckling with strength-to-weight ratios that surpass current designs. In particular, because isogrid structures are ideally suited for spacecraft, launch vehicles, and aircraft, the significant weight savings provided by the present invention allows for more payload to be delivered into orbit or for improved fuel efficiency. These and other advantages are described below with reference to the accompanying figures.